Palladium is a particularly useful metal for hydrogenation reactions. It has been utilized supported on various porous oxides substrates for the selective hydrogenation of acetylenic compounds in olefins streams without the concurrent hydrogenation of the olefins. However, when these catalysts have been used commercially, certain problems have arisen. The selectivity for the hydrogenation of the acetylene rather than the olefins is never 100%, with a certain fraction of the olefins being converted to saturated hydrocarbons. Frequently, it is desired to convert the acetylenic materials to olefins, and a highly reactive hydrogenation catalyst that would take the reaction on through to the saturated hydrocarbon would not be desirable. Olefins frequently have a higher economical value than the saturated hydrocarbons, which in many commercial applications would be utilized only for their fuel value.
U.S. Pat. No. 3,098,882, issued July 23, 1963, generally discloses the use of a palladium-chromium catalyst supported on a alumina for the selective hydrogenation of acetylene. This reference broadly discloses aluminas as supports, but does not particularly point out any special alumina as having preferred properties.
Many special forms of alumina have been utilized in order to obtain enhanced properties of the resultant catalyst. U.S. Pat. No. 4,038,175, issued July 26, 1977, discloses a palladium on an alpha-alumina support for the hydrogenation of dripolenes which are liquid unsaturated hydrocarbon by-products of a hydrocarbon cracking process for the production of ethylene. The disclosure of the support is a broad generic disclosure of low surface area alpha-alumina supports which have the following characteristics: (a) a porosity of 0.1-0.8 cc/gm; (b) a surface area of 0.1-10 m.sup.2 /g; and (c) an average pore size of 0.05-100 microns with a major portion of the pores having a pore size in the range of 0.05-10 microns.
U.S. Pat. No. 4,119,567, issued Oct. 10, 1978, discloses palladium supported on an alpha alumina support having a crystalline alpha-alumina content of greater than 96%, a surface area of 2-6 m.sup.2 /g, an average crush strength of 20-45 lbs, and a bulk density of less than 1.35 cc/g. The catalyst is disclosed as useful for the preparation of unsaturated organic esters such as vinyl and allyl acetate.
In U.S. Pat. No. 2,946,829, issued July 26, 1960, a palladium catalyst supported on an alumina carrier is disclosed wherein the alumina carrier is characterized by a pore volume of surface pores having a threshold diameter not greater than 800 .ANG. in the range from 0 to 0.4cc/g, and further characterized in that the palladium is predominately concentrated in the external portion of the carrier.
In U.S. Pat. No. 3,113,980, issued Dec. 10, 1963, there is disclosed a palladium catalyst supported on an alumina whose pores have a mean radius in the range of 100 to 1400 .ANG. units and which has a surface area in the range of 5 to 32 m.sup.2 /g.
In U.S. Pat. No. 3,116,342, issued Dec. 31, 1963, there is disclosed a palladium catalyst supported on an alumina which has pores of a mean radius of at least 100 .ANG. and not more than 1400 .ANG. and which catalyst support has a surface area in the range of 5 to 65 m.sup.2 /g.
In U.S. Pat. No. 4,126,645, issued Nov. 21, 1978, there is disclosed a palladium catalyst supported on particulate alumina having a surface area in the range of 5 to 50 m.sup.2 /g, a helium density under 5 g/cm.sup.3, a mercury density of under 1.4 g/cm.sup.3 and a pore volume of at least 0.4 cm.sup.3 /g, at least 0.1 cm.sup.3 /g of which is in the pores of radius over 300 .ANG. units, the palladium being present in the region of the catalyst particles not more than 150 microns beneath their geometric surface.
In U.S. Pat. No. 4,230,897, issued Oct. 28, 1980, there is disclosed a process for hydrogenating acetylenic hydrocarbons found in diolefinic-containing hydrocarbon streams, said hydrogenation being carried out at least partially in the liquid phase, and wherein a palladium on alumina catalyst is utilized, improvement being in this instance of utilizing the palladium on alumina catalyst wherein the average size of the palladium crystallites in said catalyst is at least 50 .ANG..
None of the references discussed herein specifically disclose the use in a catalyst of applicant's supports. The use of these supports in catalysts for the selective hydrogenation of acetylenic impurities in olefin streams provides advantages such as improved selectivities and longer periods of use before regeneration.